This invention relates to a chromatographic assay or test device for detection and/or determination of an analyte in a sample, and in one particular embodiment it relates to a chromatographic assay device which incorporates an immunoassay in a procedure known as immunochromatography.
This invention has particular, but not exclusive, application in the detection of analytes in biological samples such as blood, urine, faecal and saliva samples, and the like.
Prior International Patent Applications Nos. PCT/US92/00425(WO 92/21977) and PCT/US94/13982 (WO 95/16207) note that among the many analytical systems used for detection and/or determination of analytes, particularly analytes of biological interest, are chromatographic assay systems. Among the analytes of biological interest frequently assayed with such systems are:
1. hormones, such as human chorionic gonadotropin (hCG), frequently assayed as a marker of human pregnancy;
2. antigens, particularly antigens specific to bacterial, viral, and protozoan pathogens, such as Streptococcus, hepatitis virus, Giardia, feline leukaemia virus, tobacco mosaic virus, Salmonella, and Plasmodium;
3. antibodies, particularly antibodies induced as a result of infection with pathogens, such as antibodies to the bacterium Helicobacter pylori, to human immunodeficiency virus (HIV) and to feline immunodeficiency virus (FIV);
4. other proteins, such as haemoglobin, frequently assayed in determinations of faecal occult blood, an early indicator of gastrointestinal disorders such as colon cancer;
5. enzymes, such as aspartate amino transferase, lactate dehydrogenase, alkaline phosphatase, and glutamate dehydrogenase, frequently assayed as indicators of physiological function and tissue damage;
6. drugs, both therapeutic drugs, such as antibiotics, tranquillisers and anticonvulsants, and illegal drugs of abuse, such as cocaine, heroin, and marijuana;
7. vitamins; and
8. environmental contaminants, such as pathogens, herbicides, pesticides, toxic residues, and the like.
Such chromatographic systems are frequently used by physicians and medical technicians in the health field, and by agricultural and environmental professionals and technicians, for rapid point-of-care or on-site diagnosis, detection or monitoring of analytes of biological interest. They are also increasingly used by patients themselves for at-home monitoring of a variety of therapeutic conditions and disorders.
Among the most important of such chromatographic systems are the xe2x80x9cthin layerxe2x80x9d systems in which a solvent moves as a solvent front across a thin, flat absorbent medium. Among the most important of tests that can be performed with such thin layer systems are immunoassays, which depend on the specific interaction between an antigen or hapten and a corresponding antibody. The use of immunoassays as a means of testing for the presence and/or amount of clinically important molecules has been known for some time.
As previously noted chromatographic techniques used in conjunction with immunoassays are known as immunochromatography. In general, this technique uses a disclosing reagent or particle that has been linked to an antibody to the analyte to be assayed, forming a conjugate. This conjugate is then mixed with a specimen and, if the analyte to be assayed is present in the specimen, the disclosing reagent-linked antibodies bind to the analyte to be assayed, thereby giving an indication that the analyte to be assayed is present. The disclosing reagent or particle can be identifiable by colour, magnetic properties, radioactivity, specific reactivity with another molecule, or another physical or chemical property. The specific reactions that are employed vary with the nature of the analyte being assayed and the sample to be tested.
Although useful, currently available chromatographic techniques using test strips have a number of drawbacks. Many samples, such as faecal samples, contain particulate matter that can clog the pores of the chromatographic medium, greatly hindering the immunochromatographic process. Other samples, such as blood, contain cells and coloured components that make it difficult to read the test. Even if the sample does not create interference, it is frequently difficult with existing chromatographic test devices to apply the sample to the chromatographic medium so that the solvent front moves uniformly through the chromatographic medium to ensure that the sample reaches the area where binding is to occur in a uniform, straight-line manner.
Most immunochromatographic assay or test devices, because of their fixed and inflexible formats, are limited in their range of diagnostic applications. Most allow only unidirectional liquid flows and require that specimen or sample pre-treatments, such as antigen extraction, are carried out xe2x80x9coff-boardxe2x80x9d or prior to addition to the assay or test device.
U.S. Pat. No. 5,415,944 (assigned to Quidel Corporation) discloses a closed test device which is adapted to allow xe2x80x9con-boardxe2x80x9d pre-treatment, or extraction, of a specimen on a swab. In this case, the swab is inserted into an extraction chamber, which is moulded as part of the housing of the test device. Extraction reagents are added to the swab and, after a period of time, unidirectional flow follows passively as the reagents migrate from the chamber to the wicking components of the immunochromatographic test system encased within the housing.
International Patent Application Nos. PCT/US92/04425 and PCT/US94/13982 (assigned to SmithKline Diagnostics, Inc.) mentioned above, disclose testing systems involving sample preparation means or test components placed on the opposing panels of an open two-panel test device. In this case, the test is only initiated or completed on bringing the two opposing panels together on closure of the test device.
It is an object of the present invention to provide an assay or test device utilising a chromatographic assay format, more particularly an immunochromatographic assay format, that is versatile as well as being simple and economic to manufacture. In particular, it is an object to provide an assay or test device that utilises a closed housing in association with a moveable or relocatable element that allows manipulation of liquid flows for initiation, modification and/or completion of the assay procedure.
In accordance with a first aspect of the present invention, there is provided a chromatographic assay or test device for detection and/or determination of an analyte in a test sample, which comprises
(a) a base member, and
(b) a chromatographic medium located in or on said base member,
said base member being provided with a receptacle to receive an applicator having said sample applied thereto, said applicator being movable laterally when located in said receptacle between a first position in which said applicator located in said receptacle is out of fluid contact with said chromatographic medium, and a second position in which said applicator located in said receptacle is in fluid contact with said chromatographic medium so as to apply a sample on said applicator to said chromatographic medium.
In another aspect, the present invention provides a chromatographic assay or test device for detection and/or determination of an analyte in a test sample, which comprises
(a) a base member, and
(b) a second member,
at least one of said base member and said second member including a chromatographic medium, and said second member being movable laterally with respect to the base member from a first position to a second position, wherein in said first position a sample to be assayed applied to one of said base and second members is out of fluid contact with said chromatographic medium, and in said second position said sample is in fluid contact with said chromatographic medium.
In yet another aspect, the present invention provides a chromatographic assay or test device for detection and/or determination of an analyte in a sample, which comprises:
(a) a base member, and
(b) a second member,
at least one of said base member and said second member including a chromatographic medium, and said second member being movable laterally with respect to the base member from a first position to a second position, wherein in said first position a part of the assay of a sample using said chromatographic medium is enabled, and in said second position another part of the assay of said sample using said chromatographic medium is enabled.
Preferably, in each of the above aspects, the device of the invention is an immunochromatographic assay device which includes an immunochromatographic medium.
The present invention also extends to a method for the detection and/or determination of an analyte in a sample, characterised in that a chromatographic assay or test device as broadly described above is used in the method.
Throughout this specification and the claims which follow, unless the context requires otherwise, the word xe2x80x9ccomprisexe2x80x9d, or variations such as xe2x80x9ccomprisesxe2x80x9d or xe2x80x9ccomprisingxe2x80x9d, will be understood to imply the inclusion of a stated integer or group of integers but not the exclusion of any other integer or group of integers.
The present invention particularly relates to immunochromatographic test systems, but should not be seen as confined to these systems.
Immunochromatographic test systems typically consist of an assemblage of some or all of the following components:
a test housing with ports for addition of specimen and/or reagents, or which acts as a window for reading of a test result.
a sample receiving member eg. an absorbent matrix. This component may also effect some sample pre-treatment (eg. extraction) or some physical separation such as separating blood plasma from red cells.
a conjugate pad which contains an identifiable tag or label conjugated to a specific binding partner to the analyte of interest.
a liquid conductive solid phase (eg. nitrocellulose, nylon, etc.) to, on, or in which is immoblised a second specific binding partner of the analyte.
a liquid absorbent material to act as a specimen and reagent sink.
other conductive membranes, reagent pads or supports as required for the particular application.
In the various devices of the present invention, the base member and the second member (where present) may be made of any suitable material including, for example, plastics materials such as polycarbonate, polyethylene, Mylar, vinyl, cellophane and polystyrene, and well as water-proofed or water-resistant cardboard or similar material. Preferably, the base and second members are made of laminated cardboard that is sufficiently impervious to moisture to contain the liquids involved in the performance of the assay carried out by the device. Alternatively, the base and second members can be made of a plastic that is impervious to moisture, such as the polycarbonate plastic known as Lexan, polyvinylchloride, polypropylene, polyethylene, polystyrene, and the like.
Preferably the base member of the device of the present invention comprises upper and lower panels which are joined together to form a test housing. In the first aspect as broadly described above, the receptacle to receive an applicator such as a swab, dipstick or other sample or specimen collection device is conveniently provided in a lower panel of the base member with the chromatographic medium being attached to either the upper side of the lower panel or the lower side of the upper panel of the base member.
Where the device of this invention comprises a base member and a second member which is movable with respect to the base member, the base member preferably comprises upper and lower panels which are generally square or rectangular in shape and which are joined along opposite longitudinal edges so as to form a test housing. Preferably, the second member then comprises a generally square or rectangular planar member which is received within, and is slidably movable within, the test housing between the upper and lower panels.
The chromatographic medium in the device is typically a substantially planar strip, although this is not required in all applications. Typically, the chromatographic medium comprises a solid phase which is generally rectangular in shape having first and second ends. Throughout this description, the term xe2x80x9cfirst endxe2x80x9d refers to the end in which liquid is first applied to chromatographic medium and the term xe2x80x9csecond endxe2x80x9d applies to the opposite end of the chromatographic medium. The liquid applied at or near the first end of the solid phase of the chromatographic medium can be, but is not necessarily, a sample or a treated sample. The solid phase of the chromatographic medium is composed of an absorbent or porous material suitable as a medium for thin layer chromatography of analyte and analyte-antibody conjugates, such as nitro cellulose, nylon, rayon, cellulose, paper, silica or non-woven or porous synthetic materials. This chromatographic medium can be pretreated or modified as needed. Typically, this chromatographic medium is translucent, so that coloured zones appearing on it can be viewed from either side.
In a number of devices according to the present invention, absorbers are in operable contact with one or both ends of the chromatographic medium. Such absorbers can be made of any suitable material that will hold a liquid, particularly an aqueous liquid, sufficiently that the liquid can be drawn through the chromatographic medium and accumulated in the absorber. Typically materials for such absorbers include, but are not limited to, filter paper.
Further description of elements common to devices according to the present invention for the performance of chromatographic assays or tests are fully described in International Patent Application Nos. PCT/US92/04425 and PCT/US94/13982 mentioned above, the contents of which are incorporated herein by reference.
In a first aspect, the present invention provides a device which comprises a base member which is provided with a receptacle to receive an applicator having a test sample applied thereto. Suitably, such a receptacle is formed as an elongate well in the base member shaped to accept a swab, dipstick or similar collection device having a test sample applied thereto. The elongate well is suitably constructed that the applicator or collection device can be received within the elongate well in a first position out of liquid contact with the chromatographic medium of the test device, and at this first position the test sample on the applicator or collection device may be treated with appropriate extraction or other reagents prior to the applicator or collection device being moved within the elongate well to a second position in which it is in liquid contact with the chromatographic medium so as to apply the test sample to the chromatographic medium.
In particular embodiments, the base member in the device of the present invention may comprise separate upper and lower panels, with the chromatographic medium being attached to the upper panel and the lower panel being formed with an integral elongate well, for example by vacuum forming the lower panel from a suitable plastic material such as polyvinyl chloride. Alternatively, the lower panel may be formed of a suitable cardboard or plastic with a punched aperture defining a suitable elongate well, with a flexible fluid impervious membrane overlay being provided over the punched hole so as to define the elongate well. A preferred device in accordance with this aspect of the invention is more fully described with reference to FIGS. 1 and 2 below.
In other aspects of the present invention as broadly described above, the device comprises a base member and a second member with the second member being movable with respect to the base member from a first to a second position. Preferably, this movement is a sliding movement of the second member with respect to a test housing which comprises the base member as broadly discussed above. Preferably, also the base member provides an elongate housing and the second member is an elongate member which is slidably movable between the first and second positions within this housing. Particular embodiments of these aspects of the present invention are described in detail in FIGS. 3-8 below.